Device for moving the piston rod of a piston pump

ABSTRACT

A device for moving the piston rod of a pump in reversible longitudinal directions consists of a reversibly rotatable shaft having a radially projecting driving member secured thereon; the shaft also rotatable carries a connecting member and a driven member, the latter being connected to the piston rod; the rotation of the shaft being transmitted by the driving member to the driven member through the connecting member by springs which equalize the forces regardless of the length of the stroke of the piston rod.

United States Patent [191 Dzaack et al.

[ DEVICE FOR MOVING THE PISTON ROD OF A PISTON PUMP [75] Inventors:Heinz Dzaack, Enebyberg; Hans Krook, Sollentuna, both of Sweden [73]Assignee: LKB-Produkter AB, Bromma,

Sweden [22] Filed: Feb. 28, 1974 [21] App]. No; 446,744

[30] Foreign Application Priority Data Feb. 28, 1973 Sweden 7302785 [52]11.8. CI. 74/25 [51] Int. Cl. Fl6h 21/16 [58] Field of Search 74/25,100, 568,56

[56] References Cited UNITED STATES PATENTS 2,267,409 12/1941 Massini74/55 2,591,216 4/1952 Thompson eta]. ..74/1(10 Mar. 25, 1975 3,340,7439/1967 Stageberg 4. 74/116 3,490,309 l/l97O Gustavson 74/100 PrimaryExaminer-Wesley S. Ratliff Jr.

[57] ABSTRACT A device for moving the piston rod of a pump in reversiblelongitudinal directions consists of a reversibly rotatable shaft havinga radially projecting driving member secured thereon; the shaft alsorotatable carries a connecting member and a driven member, the latterbeing connected to the piston rod; the rotation of the shaft beingtransmitted by the driving member to the driven member through theconnecting member by springs which equalize the forces regardless of thelength of the stroke of the piston rod.

2 Claims, 2 Drawing Figures DEVICE FOR MOVING THE PISTON ROD OF A PISTONPUMP The present invention refers to a device for moving of the pistonrod of a piston pump, for instance for use in diluting different liquidvolumes in clinical laboratory investigations.

As a result of the heavily increasing quantities of samples in theclinical laboratories in recent years the requirements for a higherdegree of automization of the analysis methods used have increased. In agreat number of analyses a welbdefined quantity of a reagent is added toa liquid sample, the effect ofthe reagent on these samples thereafterbeingstudied e.g., by means of optical methods. In order to automatethis process there is a required a diluting device by means of which awell-defined quantity of the reagent can be added to the samples. Theaccuracy of this amount will have to be high for big as well as forsmall volumes and furthermore the adding of the reagent has to be fastin view of the enormous quantities of samples often at hand. It isfurthermore important that the reagent is added smoothly since it isotherwise difficult to get the sufficient accuracy. Usually the dilutionconsists in connecting a reagent vessel to a piston pump which via avalve sucks a well defined quantity of the reagent into the pumpcylinder and then sprays the reagent into the sample vessel. The pistonis thereby usually driven from a shank excentrically journalled on arotating disc, the shank being connected to the piston rod. In such adevice a smooth dilution will be obtained, since the velocity of thepiston will approximately follow a sine curve. The drawbacks of such adevice are however that it is difficult to obtain small diluting volumesof high accuracy and furthermore the diluting time will be the same forall volumes. Furthermore, the driving disc has to be stopped at the endsof the piston stroke in order to make it possible to switch the valvefrom intake to spray position or vice versa.

It is an object of the present invention to provide a driving means fora piston pump wherein the above mentioned drawbacks are eliminated. Thecharacteristics of the invention will appear from the claims attached tothe specification.

The device according to the invention will now be described in detail,reference being made to the enclosed drawing, in which:

FIG. 1 is a side view of a device according to the invention and FIG. 2is a cross-section along the driving axis at the device shown in FIG. 1.

In FIGS. 1 and 2, reference 1 denotes a driving shaft, which isalternatively rotated in opposite directions from a driving means notshown in the figures. To the shaft there is atttached a driving disc 2by means of a connecting pin 3. Close to the driving disc 2 a connectingdisc 7 is journalled on the shaft l. The driving disc 2 and theconnecting disc 7 are resiliently engaged to each other by means of adraw spring 12, having one end connected to the spring mounting 13 ofthe disc 7 and its other end connected to the spring carrier 14 of thedisc 2. By means of the tension of the spring 12 a shank 15 of the disc7 is pressed against a bent portion 16 of the disc 2. The shaft isfurther provided with a driven plate 9 journalled on the axis andprovided with a bent portion 9a which is pressed against the shank 15 ofthe connecting plate 7 by means of a spring 8 having one end connectedto a spring pin 10 of the driven plate 9 and the other end connected toa stationary frame 11. Furthermore a spring 17 is connected between thedriving disc 2 and the frame 11, the spring force of the spring 17affecting the device in a direction opposite to the direction of theforce from the spring 8.

The driven disc 9 is provided with a protruding forkshaped part 18 whichengages a roll l9'journalled on a shaft 20 attached to a rod 21 which isaxially movable within two guidings 22 and 23 respectively. The rod 21is provided with an extension arm 24 to which the piston rod (not shown)can be connected. The displacement of the rod 20 is limited by twoscrews 25 and 26, the screw 26 in practice consisting of a number ofstop pins at different levels so as to make it possible to obtaindifferent strokes of the rod 21.

The device described above operates as follows. If it is assumed thatthe rod 21 is in the position shown in FIG. 1 and the shaft 1 is drivenin the direction of the arrow A, the driving disc 2 which is attached tothe shaft will also turn and consequently also the connecting disc 7 andits shaft 15. When the shaft 15 is moving in the direction of the arrowA, the spring 8 will move the driven disc 9 in the direction of rotationofthe shaft 1 and the spring 17 will be stretched. The rod 21 will thusmove downwards till the arm 24 meets the screw 26. At this point thedriven plate 10 will stop whereas the driving plate 2 and the connectingplate 7 will move on till the direction of rotation of the shaft 1 is reversed. At this point of time the bent portion 9a of the driven plate 9has been disengaged from the shank 15 of the disc 7.

When the direction of rotation ofthe shaft 1 has been reversed thedriving disc 2 and the connecting disc 7 will move back in the directionof the arrow B. The driving means for the shaft 1 will then be assistedby the force from the spring 17. When during this movement the shank 15reaches the bent portion 9a, the driven disc 9 and thus the rod 21 willbe moved upwards. This movement continues till the rod 21 reaches thescrew 25. Thereby the movement of the driven disc 9 ceases and thus alsothe movement of the disc 7, since the shank 15 is engaged to the bentportion 9a. The driving disc 2 will however continue its rotation sinceit is fixed to the shaft 1. Thereby the spring 12 is stretched, i.e.,that the bent portion 16 is disengaged from the connecting disc 7. Thestretching of the spring will continue till the direction of rotation ofshaft 1 is reversed. After this reversal the bent portion 16 willeventually engage the shank 15 and the process described above will berepeated.

In the device described above one can simply achieve an adjustment ofdifferent desired strokes of the rod 21 and thus the stroke ota pistonconnected to the rod via the extension arm 24. This could be achieved byreplacing the single screw 26 by a number of screws of different lengthwhich by means of push buttons can be introduced into the frame 11. Bymeans of moving the screw 25 one could then make a final adjustment ofthe different volumes. A further advantage of this device consiststherein that the motor driving the shaft 1 will have approximately thesame load during each of the half-cycles of the movement of the rod 21since the force of the spring 17 has a direction opposite to the forceof the spring 8. A further advantage is that the shaft 1 continues itsrotation after the rod 21 has stopped and this movement of the axiscould be used for switching the valves in the pump, e.g., for switchingthe valve to the intake position after a spraying cycle but before theaxis is stopped in the position where the direction of rotation isreversed. This is very advantageous in such devices where the liquidstoring vessel is directly connected to the pump and the pump is movedfrom the frame together with this vessel. If the valve is not switchedthere is otherwise the risk that when storing the pump and vessel,'liquid is sprayed from the pump, e.g., due to changes of temperature orminor movements of the piston.

We claim:

1. Device for moving the piston rod of a piston pump, wherein a pistondriving rod is axially movable between two stops, at least one of saidstops being movable for obtaining different piston strokes,characterized in,

that it comprises an alternatively in two directions of rotation drivenshaft, provided with a driving disc, :1 connecting disc, journalled onsaid shaft and resiliently engaged to said driving disc and a drivendisc journalled on said axis and engaged to said rod so as to move therod axially when rotated with said shaft, said driven disc being engagedto said connecting disc by means of a spring connected between saiddriven disc and a mounting which is fixed in relation to the rotation ofsaid shaft.

2. Device according to claim 1, characterized in, that it is providedwith a spring connected between said driving disc and a mounting whichis fixed in relation to the rotation of said shaft.

1. Device for moving the piston rod of a piston pump, wherein a pistondriving rod is axially movable between two stops, at least one of saidstops being movable for obtaining different piston strokes,characterized in, that it comprises an alternatively in two directionsof rotation driven shaft, provided with a driving disc, a connectingdisc, journalled on said shaft and resiliently engaged to said drivingdisc and a driven disc journalled on said axis and engaged to said rodso as to move the rod axially when rotated with said shaft, said drivendisc being engaged to said connecting disc by means of a springconnected between said driven disc and a mounting which is fixed inrelation to the rotation of said shaft.
 2. Device according to claim 1,characterized in, that it is provided with a spring connected betweensaid driving disc and a mounting which is fixed in relation to therotation of said shaft.